Double Fano resonances in a planar pseudo-dolmen structure

•New type of nanostructure to reveal double Fano resonances was promoted and discussed.•The two dark modes can be separately adjusted.•The maximum value of FOM is 21.22, which is stronger than those of the individual plasmonic particles.

The transmittance properties of a planar pseudo-dolmen plasmonic structure were investigated using finite element method. Numerical results show that double Fano resonances are caused by the strong electric field coupling between bright and dark modes. The dark plasmon resonances are highly dependent on the structure parameters of the pseudo-dolmen structure. The Fano resonances in the pseudo-dolmen structure are also sensitive to small changes in the refractive index of the surrounding media. This characteristic could be effectively used to fabricate bi-wavelength sensors.